People talk around candles in front of the bar Voyeur in the Gaslamp District during a power outage, Sept. 8, 2011, in San Diego.

With millions of people who lost power on Sept. 8 still waiting to learn what went wrong, industry officials said Wednesday that they don't yet have answers for why the actions of one utility worker in Arizona led to a massive blackout.

Utility executives, federal investigators and officials overseeing the Southwest’s bulk power grid attended the public hearing in downtown San Diego, where state lawmakers pressed for an explanation of how the failure of a substation in Arizona could ripple across Southern California and northern Mexico, leaving 7 million people without electricity.

State Assemblyman Ben Hueso, D-San Diego, prodded for more information about root causes to little avail.

“Do you have any indication — we’re already 60 days after the event?” he said. “What failed?”

But definitive answers about events that eventually cut off power at the San Onofre Nuclear Power Generating Station are still months away, legislators learned.

“There was a cascading event that we don’t understand yet,” said Mark Maher, chief executive officer of the Western Electric Coordinating Council that oversees operators of the bulk power grid across 14 western states and portions of Mexico and Canada. “Something different happened that we weren’t able to model, that we weren’t able to see.”

A “disturbance analysis” by Maher’s office is still outstanding, and federal authorities overseeing the nation’s transmission system won’t say when they’ll be done.

But the probe over the past two months has revealed one fact, said Donald Robinson, president and chief operating officer of Arizona Public Service Co. It was wrong to pin the blame solely on a utility worker at his company’s substation, Robinson said.

“This event was not caused by the actions of a single utility worker,” he said. “That is an unfortunate perception that came out early in the process. The system is built to withstand an event like that.” Robinson said “other things should not have occurred as a result of what happened at our substation.”

The highest level inquiry into the blackout is being performed cooperatively by the Federal Energy Regulatory Commission and the North American Electric Reliability Corporation, often referred to as FERC and NERC.

Heather Polzin, an investigative division attorney at FERC, said that any speculation about the cause of the blackout is premature. She declined to say when the federal inquiry would make its results public, but noted she was taking depositions this week in San Diego.

“We are committed to finding why it did happen and preventing it from ever happening again,” she said. “We do intend to have a public report at the end of our inquiry.”

Stephen Berberich, president and chief executive officer of the California Independent System Operator that manages 80 percent of the California grid, said there was enough generation to reliably cover demand on the afternoon of the blackout, which lasted about 12 hours.

But the general manager of the Imperial Irrigation District, Kevin Kelley, described extreme 115 degree heat in the Imperial Valley between Arizona and California and "unprecedented" stress on its transmission lines leading north. The irrigation district, a community-owned electrical utility, balances its local grid independently of the California ISO.